Keyboard shortcuts

As with most editing, you can lose sight of the image-making process and become too immersed in the more complex editing functions. Keyboard shortcuts are there to help spread the load, reduce repetitive strain injury (RSI), and generally speed up your workflow. I use the first three in the following list all the time. It's also beneficial for you 
to memorize some of the tool access keys (letters) to make it easier to jump from process 
to process. Some of these are shown here:

• Ctrl/Cmd + J: Duplicate the (active) layer.
• Ctrl/Cmd + D: Use this to deselect or remove any active selection.
• Ctrl/Cmd + T: Use this to transform objects on the active layer.
• Ctrl/Cmd + E: Merge down.
• Shift + Ctrl/Cmd + E: Merge (all) visible (layers).
• O: Burn, Dodge, and Sponge tools.
• A: Selection brushes (Quick Selection, Selection Brush, Magic Wand, Refine Selection, and Auto Selection).
• L: Lasso tools (Freehand Lasso, Polygonal Lasso...